Fractionating process and apparatus



Patented Nov. 7, 1933 UNITED STATES PATENT Orr-ICE FRACTIONATING PROCESS AND APPARATUS poration of Delaware Application April 7, 1932. I Serial No. 603,639,

5 Claims.

This invention relates to improvements in the i'ractionating of relatively high and low boiling compounds from a mutual solution thereof.

It is an object oi this invention to automati- 5 cally control the reflux of a fractionating column. It is a further object to use the level of reboiler liquid to control the flow of side streams from a fracticnating tower.

Other objects will be apparent from the speciilcation and from the accompanying drawing in which latter the figure is a diagrammatic representation of a. preferred apparatus for carrying out the invention.

With a preferred embodiment in mind but without intention to limit the invention more than is required bvthe prior art, the ramnate from a solvent extraction treatment oi lube distillate is separated into a fraction comprising a substantially pure solvent and a fraction comprising substantially solvent free petroleum.

Such a raifinate may consist of apprordmatelv ten percent of the solvent which may he a pure compound such as phenol boiling at 8" F. and

90% petroleum fraction having an initial coil- 35 ing point of approximately 798 3'.

The rafinate is pumped by means ci a pump 1 through a line 2 in a furnace 3. in passing through the furnace 3 the raidnate is heated to a temperature above the boiling point oi the solvent and most of the solvent is vaporized. The heated rafiinate is passed through a line i to an intermediate portion of r. bubble tower or fractionating zone 5. The bubble tower is provided with a plurality of hell caps and overflow pipes according to the usual construction. The unvaporized portion of the ramnate flows down= wardly through the stripping section of the hubble tower. As'the ramnate flows downwardly through the bubble tower more and more of the solvent remaining in the raflinate is vaporized by the rising vapors so that the final overflow which is caught upon a pan is is substantially tree of solvent.

The overflow is delivered from the pan s through line 19 into accumulator ii. The over- 1 flow is pumped from the accumulator by a pump 13 through a iiow controller 14 in a line is into a portion oi the iurnace 3, where the liquid is heated in a reboiler circuit to a temperature in excess of that necessary to supply the additional heat required to heat the feed plate overflow in the bubble tower up to the temperature oi the contents oi the bottoms pan 6 and to vaporize the phenol in the feed. The partly vaporized discharge irom line 15 is released into the bubble tower 5 below the pan 6 whereby the vapors oi the reboiled liquid rise upwardly through the bubble tower and function to strip the low hoiling compound from the feed plate overflow. The liquid which accumulates in the bottom of the so bubble tower consists substantially of a solvent free lube fraction. This bottoms liquid is removed Irom the bubble tower through a line 17 and pump 18 at the rate at which it accumulates the tower bottom. The relooiler pump 13 is as flow controlled to deliver the accumulator liquid therethru at a constant rate several times in errcess of the rate at which the bottoms are withdrawn from the bubble tower, through the pump is. The accumulator liquid in passing through 79 the furnace 3 is subjected to a control to maintain a constant temperature at the outlet or the line 15 into the bubble tower. As a consequence, a constant heat input is supplied to the bottom of the bubble tower. The composition oi the feed oi liouldinto the accumulator is maintained suhstantially constant. The solvent or low boiling compound is withdrawn overhead from the bubble tower through a line 23 to a series of condensers 2d and 25. The so condensed solvent from condensers 2 and is delivered to containers 26 and 2'"! respectively. A portion of the condensed solvent is returned through a line 28 to the upper portion or the huhlolc tower to function as a refluxing"; agent. The remainder of the condensate is withdrawn through a line 29 to a place of storage not shown. Means are provided for controlling the delivery oi reflux through line 28 into the tower. ifhese means comprise a liquid level control as in the an accumulator 11 which is operatively connected through a line 34 with a control valve 35 in the reflux line 28. I

' By the procedure described a constant heat in put to the bottom of the bubble tower is maintained through the reboller circuit. This constant. heat input together with the preheat circuit heat input is somewhat in excess oi the heat necessary to supply the latent and sensible heat which the products have as they leave the bubble tower. This excess heat is balanced by excess reflux liquid returned to the bubble tower through the medium of the liquid level controller in the accumulator which controls the valve 35 in the rethat line. The excess reflux issu liicient to ofiset the excess heat since it condenses those oil vapors rising from the bottom 0! the tower which are in quantities over and above the quantity of oil vapors needed to vaporize the unvaporized phenol in the feed. By maintaining the excess 119 heat balanced by the excess amount 0! reflux liquid the level of liquid in the reboiler accumulator remains constant.

For moderate fluctuations in the quantity and composition of the feed, the excess heat in the, reboiling step is either diminished or increased as required by the nature of the fluctuation in feed. If a fluctuation in the quantity or composition of thefeed occurs such that more heat is required, then the excess heat is diminished. At that instant the excess quantity of reflux liquid overbalances the excess heat or the reboiler liquid,

condenses more oil vapors and causes the accumu- 'thebubble tower. A line 39 operatively connects the valve 38 with the liquid level controller 33 so that the balance between reboiler heat input and reflux cooling is maintained, during fluctuations in feed volume or composition, by regulating the amount of side stream withdrawn.

While the invention has been described as applied to the treatment of ramnate from a solvent extraction treatment of lube distillate, it will be understood that it is intended to similarly separate compounds from any source having difierent boiling points.

I claim:

1. The method of fractions-ting hydrocarbon vapors, which comprises passing the vapors through a iractionating zone whereby heavier constituents of the vapors are condensed, withdrawing unoondensed vapors from the upper portion of the zone, accumulating condensate from an intermediate portion of the zone, reheating the condensate to a constant temperature, returning the reheated condensate to the lower portion of the zone at a constant rate, condensing the withdrawn vapors, returning a portion 0! the condensed vapors to the zone as reflux, and controlling the return of reflux by the level of the accumulated condensate.

2. The method or fractionating hydrocarbon vapors, which comprises passing the vapors vapors, which comprises passing hydrocarbon vapors through a Iractionating zone whereby heavier constituents of the vapors are condensed, withdrawing uncondensed vapors from the upper portion of the zone, accumulating condensate from an intermediate portion 01' the zone, returning the condensate to the lower portion oi! the zone, reheating the returning condensate, condensing the withdrawn vapors, returning a portion of the condensed vapors to the zone as reflux, controlling the return of reflux by the level of the accumulated condensate, and withdrawing bottoms from the zone.

4. Apparatus for fractionating hydrocarbon vapors, which comprises a fractionating column, means for introducing vapors into an intermediate portion of the column, means for withdrawing uncondensed vapors from the upper portion of the column, a shell to accumulating condensate from a lower portion of the column, means for condensing the overhead vapors and for returning a portion 01' the condensate to the upper portion of the column, means actuated by the level of liquid in the shell for controlling the return of reflux, and means for reheating the accumulated condensate.

5. Apparatus for fractionating hydrocarbon 115 vapors, which comprises a fractionating column, means for withdrawing uncondensed vapors from the upper portion of the column, a shell, means for conducting condensate from the lower portion of the column to the shell, a line for conducting condensate trom the side of the column, means controlled by the level of liquid in the shell for regulating the flow through the line, means for reheating the condensate withdrawn from the shell, and means for reintroducing the reheated condensate in constant quantities'into the column.

-DAN1EL E. STINES. 

